918 research outputs found
Computing the Characteristic Polynomial of a Finite Rank Two Drinfeld Module
Motivated by finding analogues of elliptic curve point counting techniques,
we introduce one deterministic and two new Monte Carlo randomized algorithms to
compute the characteristic polynomial of a finite rank-two Drinfeld module. We
compare their asymptotic complexity to that of previous algorithms given by
Gekeler, Narayanan and Garai-Papikian and discuss their practical behavior. In
particular, we find that all three approaches represent either an improvement
in complexity or an expansion of the parameter space over which the algorithm
may be applied. Some experimental results are also presented
A solvable model for the diffusion and reaction of neurotransmitters in a synaptic junction
<p>Abstract</p> <p>Background</p> <p>The diffusion and reaction of the transmitter acetylcholine in neuromuscular junctions and the diffusion and binding of Ca<sup>2+ </sup>in the dyadic clefts of ventricular myocytes have been extensively modeled by Monte Carlo simulations and by finite-difference and finite-element solutions. However, an analytical solution that can serve as a benchmark for testing these numerical methods has been lacking.</p> <p>Result</p> <p>Here we present an analytical solution to a model for the diffusion and reaction of acetylcholine in a neuromuscular junction and for the diffusion and binding of Ca<sup>2+ </sup>in a dyadic cleft. Our model is similar to those previously solved numerically and our results are also qualitatively similar.</p> <p>Conclusion</p> <p>The analytical solution provides a unique benchmark for testing numerical methods and potentially provides a new avenue for modeling biochemical transport.</p
Evaluating the Effect of Crutch-using on Trunk Muscle Loads
As a traditional tool of external assistance, crutches play an important role
in society. They have a wide range of applications to help either the elderly
and disabled to walk or to treat certain illnesses or for post-operative
rehabilitation. But there are many different types of crutches, including
shoulder crutches and elbow crutches. How to choose has become an issue that
deserves to be debated. Because while crutches help people walk, they also have
an impact on the body. Inappropriate choice of crutches or long-term misuse can
lead to problems such as scoliosis. Previous studies were mainly experimental
measurements or the construction of dynamic models to calculate the load on
joints with crutches. These studies focus only on the level of the joints,
ignoring the role that muscles play in this process. Although some also take
into account the degree of muscle activation, there is still a lack of
quantitative analysis. The traditional dynamic model can be used to calculate
the load on each joint. However, due to the activation of the muscle, this
situation only causes part of the load transmitted to the joint, and the work
of the chair will compensate the other part of the load. Analysis at the muscle
level allows a better understanding of the impact of crutches on the body. By
comparing the levels of activation of the trunk muscles, it was found that the
use of crutches for walking, especially a single crutch, can cause a large
difference in the activation of the back muscles on the left and right sides,
and this difference will cause muscle degeneration for a long time, leading to
scoliosis. In this article taking scoliosis as an example, by analyzing the
muscles around the spine, we can better understand the pathology and can better
prevent diseases. The objective of this article is to analyze normal walking
compared to walking with one or two crutches using OpenSim software to obtain
the degree of activation of different muscles in order to analyze the impact of
crutches on the body
The Study of TeV Variability and Duty Cycle of Mrk 421 from 3 Years of Observations with the Milagro Observatory
TeV flaring activity with time scales as short as tens of minutes and an
orphan TeV flare have been observed from the blazar Markarian 421 (Mrk 421).
The TeV emission from Mrk 421 is believed to be produced by leptonic
synchrotron self-Compton (SSC) emission. In this scenario, correlations between
the X-ray and the TeV fluxes are expected, TeV orphan flares are hardly
explained and the activity (measured as duty cycle) of the source at TeV
energies is expected to be equal or less than that observed in X-rays if only
SSC is considered. To estimate the TeV duty cycle of Mrk 421 and to establish
limits on its variability at different time scales, we continuously observed
Mrk 421 with the Milagro observatory. Mrk 421 was detected by Milagro with a
statistical significance of 7.1 standard deviations between 2005 September 21
and 2008 March 15. The observed spectrum is consistent with previous
observations by VERITAS. We estimate the duty cycle of Mrk 421 for energies
above 1 TeV for different hypothesis of the baseline flux and for different
flare selections and we compare our results with the X-ray duty cycle estimated
by Resconi et al. 2009. The robustness of the results is discussed.Comment: 27 pages, 6 figures, ApJ accepte
Spectrum and Morphology of the Two Brightest Milagro Sources in the Cygnus Region: MGRO J2019+37 and MGRO J2031+41
The Cygnus region is a very bright and complex portion of the TeV sky, host
to unidentified sources and a diffuse excess with respect to conventional
cosmic-ray propagation models. Two of the brightest TeV sources, MGRO J2019+37
and MGRO J2031+41, are analyzed using Milagro data with a new technique, and
their emission is tested under two different spectral assumptions: a power law
and a power law with an exponential cutoff. The new analysis technique is based
on an energy estimator that uses the fraction of photomultiplier tubes in the
observatory that detect the extensive air shower. The photon spectrum is
measured in the range 1 to 200 TeV using the last 3 years of Milagro data
(2005-2008), with the detector in its final configuration. MGRO J2019+37 is
detected with a significance of 12.3 standard deviations (), and is
better fit by a power law with an exponential cutoff than by a simple power
law, with a probability % (F-test). The best-fitting parameters for the
power law with exponential cutoff model are a normalization at 10 TeV of
, a spectral
index of and a cutoff energy of TeV. MGRO
J2031+41 is detected with a significance of 7.3, with no evidence of a
cutoff. The best-fitting parameters for a power law are a normalization of
and a
spectral index of . The overall flux is subject to an
30% systematic uncertainty. The systematic uncertainty on the power law
indices is 0.1. A comparison with previous results from TeV J2032+4130,
MGRO J2031+41 and MGRO J2019+37 is also presented.Comment: 11 pages, 10 figure
Calibration of the Milagro Cosmic Ray Telescope
The Milagro detector is an air shower array which uses the water Cherenkov
technique and is capable of continuously monitoring the sky at energies near 1
TeV. The detector consists of 20000 metric tons of pure water instrumented with
723 photo-multiplier tubes (PMTs). The PMTs are arranged in a two-layer
structure on a lattice of 3 m spacing covering 5000 area. The direction
of the shower is determined from the relative timing of the PMT signals,
necessitating a common time reference and amplitude slewing corrections to
improve the time resolution. The calibration system to provide these consists
of a pulsed laser driving 30 diffusing light sources deployed in the pond to
allow cross-calibration of the PMTs. The system is capable of calibrating times
and the pulse-heights from the PMTs using the time-over-threshold technique.
The absolute energy scale is provided using single muons passing through the
detector. The description of the calibration system of the Milagro detector and
its prototype Milagrito will be presented.Comment: 4 pages, submitted to the XXVI International Cosmic Ray Conferenc
Study of the Shadows of the Moon and the Sun with VHE Cosmic Rays
Milagrito, a prototype for the Milagro detector, operated for 15 months in
1997-8 and collected 8.9 billion events. It was the first extensive air shower
(EAS) array sensitive to showers intiated by primaries with energy below 1 TeV.
The shadows of the sun and moon observed with cosmic rays can be used to study
systematic pointing shifts and measure the angular resolution of EAS arrays.
Below a few TeV, the paths of cosmic rays coming toward the earth are bent by
the helio- and geo-magnetic fields. This is expected to distort and displace
the shadows of the sun and the moon. The moon shadow, offset from the nominal
(undeflected) position, has been observed with high statistical significance in
Milagrito. This can be used to establish energy calibrations, as well as to
search for the anti-matter content of the VHE cosmic ray flux. The shadow of
the sun has also been observed with high significance.Comment: 4 pages, submitted to XXVI International Cosmic Ray Conference, Salt
Lake Cit
Evidence for TeV Emission from GRB 970417a
Milagrito, a detector sensitive to very high energy gamma rays, monitored the
northern sky from February 1997 through May 1998. With a large field of view
and a high duty cycle, this instrument was well suited to perform a search for
TeV gamma-ray bursts (GRBs). We report on a search made for TeV counterparts to
GRBs observed by BATSE. BATSE detected 54 GRBs within the field of view of
Milagrito during this period. An excess of events coincident in time and space
with one of these bursts, GRB 970417a, was observed by Milagrito. The excess
has a chance probability of of being a fluctuation of the
background. The probability for observing an excess at least this large from
any of the 54 bursts is . No significant correlations were
detected from the other bursts.Comment: 10 pages, 3 figure
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